Synthesis and proton NMR spectroscopic characterization of trans-[Pt(NH3)2[d(ApGpGpCpCpT)-N7-A(1),N7-G(3)]]

Abstract

The reaction of trans-[Pt(NH3)2Cl2] with the sodium salt of [d(ApGpGpCpCpT)]2 in aqueous solution at 37 degrees C was monitored by reversed-phase high-performance liquid chromatography and UV spectroscopy. Two intermediates, most likely monofunctional adducts, were observed, which subsequently formed one predominant single-stranded product, as well as several polymeric species proposed to be interstrand cross-linked products. The single-stranded adduct was structurally characterized by 1H NMR spectroscopy. From the pH dependence of the chemical shifts, two-dimensional homonuclear chemical shift correlation (COSY) spectroscopy, and one- and two-dimensional nuclear Overhauser effect (NOESY) experiments, the platinum(II) moiety was found to be coordinated to the N7 positions of adenine(1) and guanine(3), with the intervening guanine(2) base destacked from its neighboring residues. This intrastrand 1,3 adduct induces changes in the backbone torsion angles and causes the deoxyribose ring of adenine(1) to switch from a C2'-endo to a predominantly C3'-endo conformation. The other deoxyribose rings retain B DNA type conformations. The structure of trans-[Pt(NH3)2[d(ApGpGpCpCpT)-N7-A(1),N7-G(3)]] differs from those previously reported for cis-DDP 1,2- and 1,3-intrastrand oligonucleotide adducts but is consistent with the structures of trans-DDP 1,3-intrastrand adducts of two previously reported trinucleotides.

Inhibition of transcription by platinum antitumor compounds

“…Minor products included 1,2-d(GpG) (30%), 1,2-d(ApG) (16%), as well as a small number of interstrand (3–4%) cross-links and monofunctional adducts. Because trans -diamminedichloroplatinum(II) is incapable of forming 1,2-intrastrand cross-links on DNA,32, 33 and because this complex has insignificant antitumor activity in cells,34 intrastrand adducts are more likely to be responsible for the cytotoxicity of cisplatin in cancer cells. Further investigations of platinum interstrand cross-links revealed no correlation between the frequency of ICL formation and cytotoxicity, providing additional evidence that intrastrand cross-links are essential to tumor cell death 35…”

DNA double helix promotes a linkage isomerization reaction in trans-diamminedichloroplatinum(II)-modified DNA.

“…Among the differences between the two isomers, one is that stereochemical limitations preclude trans-DDP from forming intrastrand cross-links between adjacent base residues (10). The most prevalent adducts are intrastrand cross-links between two G residues and between G and cytosine (C) residues separated by at least one residue (11)(12)(13). Another difference is that trans-DDP forms the interstrand cross-links preferentially between complementary G and C residues (14).…”

On the Mechanism of Action of the Antitumor Drug cis‐Platin(cis‐DDP) and its Second Generation Derivatives

“…Atomic absorption spectroscopy 9ave the value k=(5.4+_0.4) XlO sec [115], for the rate constant of the reaction of DNA with trans-DDP [148], while it is reminded that the rate constant for the replaemen of the first chlorine by a water molecule (Fig. 6) was k.'=1.9 X 10 sec This l indicates that trans-DDP binds to DNA in two pseudofirst order steps, the first being the chlorine replacement and the formation of a monodentate complex with the N7 of guanine and the second, which is faster, the formation of the 17-membered chelate through the N7 atoms of e(5) and of the nucleotide [148].…”